Valve assembly with cage and flow control assembly

ABSTRACT

A valve assembly is provided, the assembly comprising a valve housing; an inlet for fluid entering the valve housing; an outlet for fluid leaving the valve housing; a flow control assembly disposed within the valve housing between the inlet and the outlet, whereby fluid entering the valve housing is caused to flow through the flow control assembly, the flow control assembly comprising a cage having apertures therethrough to provide passage for fluid passing from the inlet to the outlet, the cage having a longitudinal axis and an outlet end, in use fluid generally flowing within the cage in a downstream direction towards the outlet end; a closure assembly moveable with respect to the cage to open or close each of the apertures through the cage, to thereby control the flow of fluid through the cage; wherein the apertures in the cage extend through the cage at a first angle being an angle to the longitudinal axis of the cage in the upstream direction. A cage for use in a valve assembly is also provided.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit of Great BritainApplication No. GB1423203.7, entitled “VALVE ASSEMBLY”, filed Dec. 24,2014, which is herein incorporated by reference in its entirety.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

The present invention relates to a valve assembly, in particular to avalve assembly having a flow control element of the plug and cage typearrangement, and to the use of the valve assembly in the processing offluid streams. The present invention further relates to a wellheadassembly comprising the valve assembly, in particular a subsea wellheadassembly.

Valve assemblies are well known and widely used in an extensive range offluid processing applications. Valves are used to control the flow of afluid stream, for example to control the flow rate and/or pressure ofthe fluid stream.

One common valve assembly comprises a flow control element having aso-called ‘plug and cage’ arrangement. This assembly has a cage,typically cylindrical in form, comprising a plurality of holes orapertures therethrough for the passage of fluid. A plug, again generallycylindrical in form, is provided so as to be moveable with respect tothe cage, the plug being disposed to be moveable to cover or close theapertures in the cage. The plug may be moved with respect to the cagebetween a closed position, in which all the apertures in the cage arecovered, thus preventing fluid from flowing through the choke assembly,and a fully open position, in which all the apertures in the cage areopen and available for fluid flow. Moving the plug with respect to thecage from the closed to the fully open position progressively uncoversthe apertures in the cage, thus increasing the cross-sectional areaavailable for fluid flow. In this way, the flow rate and pressure of thefluid may be varied and controlled. In the closed position, the endsealing portion of the plug contacts a seat formed in the chokeassembly, so as to provide a fluid-tight seal, preventing the passage offluid past the plug and cage. The plug may be arranged coaxially withinthe cage or coaxially exterior of the cage, known in the art as anexternal sleeve.

FR 2 436 922 discloses a valve for controlling the flow of a fluid, thevalve comprising a housing having an inlet for fluid. The inlet isdisposed in the wall of the housing and fluid flow through the inlet iscontrolled by a vane pivotably mounted at one side of the opening. Fluidleaves the housing through a centrally disposed outlet.

A fluid flow choke is disclosed in GB 2 124 341 and has a stationarytubular flow nozzle with throttling ports formed in a side wall thereof.A moveable throttling ring is moved over the nozzle to restrict or closethe ports.

DE 36 15 432 concerns a flow valve having a slide gate moveable to alignwith a flow opening. The slide gate has an opening therein that has across-sectional area matched to that of the flow opening, such that asubstantially constant response sensitivity is obtained across the rangeof settings of the valve.

A balanced sleeve control choke is described and shown in U.S. Pat. No.5,086,808. The choke has a cage provided with openings therein and anexterior sleeve moveable over the cage to open and close the openings,thereby controlling the flow of fluid through the cage.

A valve having a closure member for creating turbulence in the flow ofliquid through the valve is disclosed in U.S. Pat. No. 5,617,896.

U.S. Pat. No. 5,979,558 discloses a variable choke for use insubterranean well. The choke comprises an inner sleeve with openingstherein, moveable with respect to an outer sleeve.

An apparatus and method for controlling the flow of a fluid is disclosedin WO 01/02697. The apparatus comprises a valve assembly having anorifice therein through which fluid flows. The orifice is shaped toprovide a substantially consistent or otherwise predetermined change inpressure drop and flow rate between different positions of the valve.This is achieved by the orifice being shaped to provide a non-linearvariation in the flow area throughout several positions of the valve.

US 2002/0020534 discloses a flow control device having inner and outersleeves moveable with respect to each other and both provided withopenings therein for the flow of fluid. The fluid flow is controlled byappropriate positioning of the inner and outer sleeves relative to eachother.

A well choke is disclosed in US 2007/0095411. The choke is of a plug andcage design and has a quick closure device mounted between an actuatorand the choke.

A flow control valve for gaseous or liquid media is disclosed in DE 3717 128. The flow control valve comprises a plug and cage assemblyarranged within a fluid inlet chamber. The plug and cage assembly isoffset from the central longitudinal axis of the inlet chamber. The cagecomprises a plurality of openings arranged in the wall of the cage. Oneportion of the cage comprises six openings extending horizontallythrough the cage, that is perpendicular to the longitudinal axis of thecage, at a tangent to the inner surface of the cage. Fluid flow throughthe openings in the cage is controlled by the position of the plugwithin the cage. A delivery chamber is disposed immediately downstreamof the cage and is provided with a retarder to stop rotational flow ofthe fluid and produce a linear fluid flow pattern leaving the device.

More recently, EP 2 386 717 discloses a valve assembly of the plug andcage arrangement. The cage of the valve assembly is provided with aplurality of apertures therein, with the flow of fluid through the cagebeing controlled by the position of the plug within the cage. Theapertures in the cage are arranged into rows, each row having one ormore apertures. The rows of apertures are separated by lands, in whichno apertures are present. In this way, the plug may be positioned withinthe cage such that its end face aligns with a land and does not extendacross an aperture. In this position, each aperture is either fully openor fully closed. An advantage of this arrangement is that the erosion ofthe end face of the plug is significantly reduced. The apertures mayextend tangentially to the inner wall of the cage.

EP 2 386 717 also discloses for the first time the formation of fluidbands within the cage of the valve assembly by fluid entering throughthe apertures. Each row of apertures can form a band of rotating fluidwithin the cage. The fluid bands act as hydraulic chokes, throttling theflow of fluid in the downstream direction within the cage.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, aspects, and advantages of the present invention willbecome better understood when the following detailed description is readwith reference to the accompanying figures in which like charactersrepresent like parts throughout the figures, wherein:

FIG. 1 is a cross-sectional view of a valve assembly according to afirst embodiment of the present invention;

FIG. 2 is a cut-away, cross-sectional view of the lower housing of thevalve assembly of FIG. 1;

FIG. 3 is a diagrammatical cross-sectional view of the lower housing ofthe valve assembly along the line III-III of FIG. 2;

FIGS. 4a, 4b, 4c and 4d are diagrammatical cross-sectional views of thechannel in the inner wall of the lower housing of the valve assembly ofFIG. 2, at the positions A, B, C and D respectively of FIG. 3;

FIG. 5 is a cross-sectional view of the lower housing of the valveassembly of FIG. 1, showing the flow control assembly therein;

FIG. 6 is a cross-sectional view of a portion of the flow controlassembly of FIG. 1 in the fully closed position;

FIG. 7 is an enlarged cross-sectional view of the seating arrangement ofthe flow control assembly shown in FIG. 6;

FIG. 8 is a cross-sectional view as in FIG. 6, but with the flow controlassembly in a position intermediate between the fully closed positionand the fully open position;

FIG. 9 is a detailed cross-sectional view of the assembly of FIG. 1,showing a first portion of the actuator mechanism;

FIG. 10 is a detailed cross-sectional view of the assembly of FIG. 1,showing a second portion of the actuator mechanism;

FIG. 11 is a vertical cross-sectional view of a portion of the cage andthe end portion of the closure assembly of the apparatus of FIG. 1;

FIG. 12 is a horizontal cross-sectional view of the cage of FIG. 11through a row of apertures of the cage and showing the general patternof fluid flow through the wall of the cage; and

FIG. 13 is a vertical cross-sectional view of a cage and plug assemblyof a further embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. These described embodiments are only exemplary of thepresent invention. Additionally, in an effort to provide a concisedescription of these exemplary embodiments, all features of an actualimplementation may not be described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

It would be advantageous if an improved design of valve could beprovided, in particular an improved design of a valve employing a plugand cage arrangement. It would be of particular advantage if the valvecould provide a high efficiency in the control of fluid flowing throughthe valve at all positions of the valve between the fully closedposition and the fully open position.

It has now been found that an improved valve is one provided with a cagedisposed between a fluid inlet and a fluid outlet and having aperturestherein through which fluid is caused to flow. It has been found that animproved performance of the valve in controlling both the flowrate andpressure of fluid flowing through the valve if the fluid entering theinterior of the cage is caused to flow first in an upstream direction,away from the fluid outlet, in an outer region of the cage interior and,thereafter, to flow in a downstream direction towards the fluid outletin an inner or central region of the cage interior.

According to the present invention, therefore, there is provided a valveassembly comprising:

a valve housing;

an inlet for fluid entering the valve housing;

an outlet for fluid leaving the valve housing;

a flow control assembly disposed within the valve housing between theinlet and the outlet, whereby fluid entering the valve housing is causedto flow through the flow control assembly, the flow control assemblycomprising:

a cage having apertures therethrough to provide passage for fluidpassing from the inlet to the outlet, the cage having a longitudinalaxis and an outlet end, in use fluid generally flowing within the cagein a downstream direction towards the outlet end;

a closure assembly moveable with respect to the cage to open or closeeach of the apertures through the cage, to thereby control the flow offluid through the cage;

wherein the apertures in the cage extend through the cage at a firstangle being an angle to the longitudinal axis of the cage in theupstream direction.

The valve assembly comprises a housing having an inlet for fluid and anoutlet for fluid, with a flow control assembly disposed within thehousing between the fluid inlet and fluid outlet. In one preferredarrangement, the valve assembly is arranged whereby all the fluidentering the housing through the inlet is caused to flow through theflow control assembly to the fluid outlet.

In a preferred arrangement, the housing comprises a cavity therein, theflow control assembly being disposed within the cavity, for examplecentrally, such that the cavity extends around the flow controlassembly. In this way, fluid entering through the fluid inlet in thehousing is caused to flow around the flow control assembly and enter thecage evenly from the cavity. In a preferred arrangement, to assist theeven distribution of fluid within the cavity, the fluid inlet isarranged in the housing to extend tangentially to the walls of thecavity. It has been found that such an arrangement having a tangentialentry provides an improved fluid control when using the sleeve/cagearrangement of the valve assembly of the present invention. Inparticular, by directing incoming fluid into the cavity at an angle, thedirect impact of the fluid onto the portion of the flow control assemblyfacing the inlet is avoided. This prevents premature wear and failure ofthe flow control assembly, in particular in the case of an erosive fluidstream, such as one containing entrained solid particles, such as may beproduced from a subterranean well from time to time. In addition, byhaving the fluid stream directed in the cavity around the flow controlassembly, a more even flow of fluid through the flow control assembly isobtained, in turn improving the control of the fluid flowrate and/orpressure.

In a particularly preferred arrangement, the inlet has the form of anopening in the wall of the cavity, disposed to direct fluid into achannel or groove having the form of an involute and extending aroundthe outer wall of the cavity. The channel or groove is formed to have aprogressively smaller cross-sectional area, in order to progressivelyintroduce fluid into the cavity around the flow control assembly. Inthis way, an even distribution of fluid around the flow control assemblyis obtained.

As noted, the valve assembly comprises an inlet and an outlet for fluidto enter and leave the valve housing. Between the inlet and the outletis disposed a flow control assembly, operable to control the flow rateand/or pressure of fluid passing through the valve. The flow controlassembly comprises a cage having apertures therethrough, through whichfluid is caused to flow. The apertures are opened and closed by movementof the closure assembly, as described hereafter. In particular, theclosure member is movable between a fully closed position, in which allof the apertures in the cage wall are covered by the closure assembly,and a fully open position in which all of the apertures in the cage wallare open or uncovered by the closure assembly. The control of the flowof fluid is obtained by selecting the number and/or size of aperturesthat are open for fluid passage.

The cage may have any suitable form, but is preferably in the form of agenerally cylindrical tube, with apertures extending through the wall ofthe tube.

In use, fluid enters the interior of the cage through the apertures andflows to the fluid outlet. In this respect, the general direction offlow of fluid within the cage is in a downstream direction towards theoutlet, that is the direction of flow of the bulk fluid from theapertures in the cage to the fluid outlet. The fluid may deviate fromthis general bulk direction of flow within the cage, as describedhereinafter. However, all fluid entering the cage through the aperturesleaves the cage at its outlet end. References herein to the upstreamdirection within the cage are to be understood accordingly.

The apertures may extend through the wall of the cage and be arrangedaround the cage in any suitable pattern. Known patterns for theapertures include overlapping rows of apertures of different sizes. Inone preferred arrangement, the apertures are arranged in a plurality ofrows, each row containing one or more apertures, with adjacent rowsbeing separated by a land or region having no apertures therethrough.This arrangement improves the accuracy of the control of fluid flow, byallowing the closure assembly, such as a plug or sleeve, to lie with itsend face extending across the land, thereby leaving the apertures eitherfully open or fully closed, depending upon their position relative tothe plug or sleeve. In addition, the option of having the end face ofthe plug or sleeve in a position where it does not extend across apartially open aperture allows the end face of the sleeve or plug to beprotected from the stream of fluid passing through the aperture. Inknown arrangements, it is frequently the case that the end faces ofplugs and sleeves are eroded by the streams or jets of fluid formed asthe fluid passes through the apertures in the cage. These streams orjets can quickly erode the plug or sleeve, in particular eroding thesurface of the plug or sleeve that contacts the seat in the fully closedposition. This in turn reduces the ability of the plug or sleeve to forma complete seal to prevent fluid flow when fully closed. This effect isreduced or minimized by having the apertures arranged in rows, separatedby lands, as described above.

The apertures extending through the cage of the valve assembly of thepresent invention extend at an angle to the longitudinal axis of thecage, herein referred to as the first angle, and extend from the outersurface of the cage to the inner surface in the upstream direction. Theangle is in a longitudinal plane containing the longitudinal axis of thecage and extending perpendicular to a lateral plane containing a radiusof the interior of the cage.

The effect of having the apertures extending at the angle to thelongitudinal axis is to direct the fluid entering the interior of thecage in an initial upstream direction within the cage. As a result,fluid entering the cage through the upstream facing apertures isinitially directed both radially inwards into the interior of the cageand in an upstream direction. Thereafter, the fluid continues to flowradially inwardly, with the longitudinal direction of fluid flowchanging from upstream to downstream. As a result, the fluid flowing inthe radially inner portion of the cage is flowing in a downstreamdirection towards the fluid outlet. It has been found that a fluid flowpattern within the cage, in which the longitudinal direction of fluidflow is caused to change from an upstream flow to a downstream flow,gives rise to an improved control over fluid flowing through theassembly. In particular, by causing the fluid flowing within the cage tochange its direction of flow from upstream to downstream gives rise to apartial hydraulic lock within the cage, in turn giving rise to a backpressure on the incoming fluid.

The angle of the aperture to the longitudinal axis may be any suitableangle. The apertures in the wall of the cage may extend at differentangles, for example depending upon their location in the wall.Preferably, all the apertures in the cage extend at the same angle tothe longitudinal axis.

Preferably, the angle to the longitudinal axis is less than 85°, morepreferably less than 80°, still more preferably less than 75°. In manyembodiments, an angle of less than 70° is preferred. One preferredembodiment has the apertures extending at an angle of 65° to thelongitudinal axis. An angle in the range of from 50° to 80°, morepreferably from 60° to 70°, has been found to provide an advantageousarrangement in terms of the number, size and arrangement of theapertures in the cage, together with providing an advantageous size ofcage.

As noted above, in operation of the valve assembly of the presentinvention, the fluid entering the interior of the cage through theapertures in the cage is caused to flow first in an upstream direction,that is away from the fluid outlet, and thereafter undergo a reverse inthe direction of flow to a downstream direction towards the fluidoutlet. The length of time the fluid spends flowing in the upstreamdirection and the length of the upstream fluid flowpath within the cageis dependent, at least in part, on the angle of the apertures in thecage to the longitudinal direction. In particular, it has been foundthat increasing the angle of the apertures to the longitudinaldirection, that is as the angle approaches 90° or flow radiallyinwardly, the time of upstream fluid flow and the length of the upstreamfluid flowpath is reduced. Conversely, reducing the angle of theapertures to the longitudinal axis increases the time of upstream fluidflow and the length of the upstream fluid flowpath within the cage.Increasing the length of time of the upstream fluid flow and the lengthof the upstream fluid flowpath increases the fluid pressure drop betweenthe exterior of the cage and the fluid outlet. In this way, the extentof pressure drop experienced by a given set of fluid flow conditionsthrough the assembly may be varied during the design of the cage, byvarying the angle of the apertures in the cage to the longitudinaldirection.

The length of the upstream fluid flowpath within the cage of theassembly may be selected to provide the required fluid flow control, asdescribed above. Preferably, the length of the upstream fluid flowpath,that is the distance travelled by fluid entering the cage through theapertures in the cage in the upstream direction is at least the same asthe inner diameter of the fluid flow region within the cage. With theassembly in the fully open position, the length of the upstream fluidflowpath is preferably greater than the inner diameter of the cage.

The apertures in the cage of the valve assembly preferably also extendthrough the wall of the cage at an angle to the radial direction of thecage, herein referred to as the second angle. In this respect, theradial direction is to be taken as being a line extending normal to theinner surface of the cage and extending perpendicular to the centrallongitudinal axis of the cage. In particular, the second angle is anangle measured in a lateral plane of the cage extending perpendicular tothe longitudinal axis of the cage.

The effect of having the apertures in the cage extend at an angle to theradial direction is to direct fluid entering the cage through theapertures around the interior of the cage, so as to form a rotating orswirling fluid flow pattern around the inner surface of the wall of thecage. This is in contrast to conventional designs, in particular ofchokes, in which the apertures extend radially through the cage wall,the result of which is to direct fluid entering the cage through theapertures radially inwards and directly at the center of the cage. Thisin turn results in the incoming fluid streams being subject tosignificant shear. In the case of such valves being used to processfluid streams having a plurality of fluid phases, this in turn resultsin a very high degree of mixing of the fluid phases. This is undesirablein the case of fluid streams being processed that are to be subjected toseparation downstream of the valve assembly, such as is the case withfluid streams comprising oil, gas and/or water produced fromsubterranean wells. The fluid flow patterns generated within the cage ofthe valve assembly of the present invention are advantageously subjectedto lower shear, as a result of being directed around the interior of thecage.

In particular, as a result of the combined effects of the aperturesextending at the first angle to the longitudinal axis and the secondangle to the radial direction, the incoming fluid is caused to flow in aspiral or helical pattern in the upstream direction within the cage.

In a preferred embodiment, the apertures are angled to both thelongitudinal axis of the cage, that is the first angle, and to theradial direction, that is the second angle. In this embodiment, theangle of the apertures to the longitudinal axis is preferably selectedsuch that fluid entering the interior of the cage through a firstaperture is guided around the interior of the cage to pass above thestream of fluid entering the cage through a second aperture adjacent thefirst and in the same lateral plane as the first aperture. In thisrespect, the term ‘above’ is a reference to a distance in the upstreamdirection within the interior of the cage. With the apertures arrangedas in this embodiment, the spacing of adjacent apertures and the angleof the apertures are related. In particular, with the apertures spacedfurther apart, the angle of the aperture to the longitudinal axis can bereduced and still have the fluid stream from the first apertures passabove the adjacent second aperture. Similarly, a larger angle isrequired if the apertures are spaced closer together.

The angle of the aperture to the radial direction may be any suitableangle to the radial direction. For example, the second angle may be atleast 10° to the radial direction, more preferably at least 20°, stillmore preferably at least 30°. Preferably, the second angle is at least45°, more preferably at least 60°, still more preferably at least 70° tothe radial direction. In a particularly preferred embodiment, the secondangle is such that the apertures open at a tangent to the inner surfaceof the wall of the cage.

In general, a flow pattern within the cage giving rise to rotating fluidbands or impingement of the incoming jets of fluid gives rise to asignificant back pressure, in turn creating a high fluid pressure dropacross the valve from the inlet to the outlet. This effect is used whenthe valve is being used to control pressure, such as is the case with achoke assembly. Such an assembly may be classed as a pressure controldevice.

However, there is also a need to control the flow of fluid through thevalve, that is have the valve perform as a flow control device. In thistype of operation, the flow of fluid through the valve should occur viathe easiest and smoothest path. The valve of the present invention isarranged to be a flow control device to control the flow of a fluidstream, for example to control the commingling of fluid from differentsources upstream or downstream of a process system, such as a separator.

In the valve assembly of the preferred embodiment of the presentinvention, the tangentially extending, upstream directed ports allow thefluid to follow a swirling flow pattern within the cage having a minimumof shear flow, eddie flow or cross-flow. By appropriate arrangement ofthe apertures in the cage, for example in a plurality of rows, a smoothflow control curve is achieved, that is the change in flow of fluidthrough the valve with changes in the position of the closure assemblyis a smooth curve. In particular, the form of the apertures allows forthe fluid jet entering the cage from one aperture to avoid overlappingthe jet from an adjacent aperture, reducing the occurrence of fluidshear. Further, the jets from adjacent apertures can be spaced a minimumdistance apart, reducing the occurrence of eddie flows.

It may be the case that a significant fluid pressure drop is requiredacross the device, depending upon the processing requirements. The valveassembly of the present invention also allows for such a pressure dropto be achieved, but without significant fluid shear or eddie currents orfoaming, as noted above. This is in contrast to known valve assemblieswhen partly open, such as butterfly valves, ball valves or gate valves.

The apertures in the wall of the cage may be of any suitable shape. Inthis respect, the term ‘shape’ refers to the cross-sectional form of theaperture taken along the outer or inner surface of the cage wall.Examples of suitable shapes include circular and elliptical. In apreferred embodiment, the apertures are quadrilateral in shape. Forexample, the apertures may be rectangular in shape. It has been foundthat a rectangular shape for the apertures provides an advantageousfluid flow pattern within the cage. However, with the cage beingcylindrical in shape, the curved wall of the cage increases thedimensions of the aperture in the longitudinal direction of the cage.This in turn increases the length of the cage and, as a result, theoverall size of the assembly to accommodate the increased cage length.In particular, an increase in the length of the cage requires acorresponding increase in the distance the closure assembly, is requiredto be moved within the cage and, hence, the length of the actuatormechanism.

It has been found that this effect can be reduced or eliminated if theshape of the apertures deviates from a rectangle. Accordingly, in apreferred arrangement, the apertures are in the shape of aparallelogram. More preferably, the apertures are rhomboidal in shape.It has been found that rhomboidal apertures allow the required area ofthe apertures to be maintained, without a significant increase in theoverall size of the apertures and a resultant increase in the length ofthe cage.

The angle between the sides of the parallelogram apertures will bedetermined by such factors as the first angle of the aperture. Forexample, an aperture having four equal sides of 2.5 cm (1.0 inch) andextending at a first angle of 65°, with four apertures in a row in acage of nominal diameter of 15 cm (6 inches) has an angle between thesides of about 48°. The angle of the parallelogram is preferablyselected to form a rectangular opening of the aperture in the interiorwall of the cage. In this way, the apertures may be arranged in rowswith lands therebetween, according to a preferred embodiment of thepresent invention.

As noted above, the cage is generally cylindrical, having a wall that iscurved in the circumferential direction. In order to provide the optimumflow pattern of fluid entering the cage through the apertures, it ispreferred to accommodate the curvature of the cage wall by providing theupstream and/or downstream edges of the aperture with a correspondingcurve. Preferably, both the upstream and downstream edges (hereinafterthe ‘upper’ and ‘lower’ edges) are curved. This arrangement provides thecage with the shortest length, for a given number and size of apertures.Accordingly, the apertures may be rectangular, having upper and lowercurved edges, more preferably a parallelogram shape having curved upperand lower edges. It is particularly preferred for the apertures to berhomboidal in shape with upper and lower curved edges. With the upperand lower edges of the aperture curved in the aforementioned manner, thefluid stream entering the interior of the cage through the aperture isgenerally rhomboidal in form.

As also noted above, the apertures may be arranged in the cage wall inany suitable pattern, with the apertures arranged in rows beingpreferred, more preferably with a land having no apertures thereinprovided between adjacent rows of apertures in the cage. As also notedabove, each aperture in the cage extends at a first and, preferably, asecond angle. At least some of the apertures in the cage are preferablyarranged, in terms of their first and second angles, and theirarrangement around the wall of the cage such that the fluid streamentering the cage through one aperture flows at least partially abovethe adjacent aperture in the same row in the direction of flow withinthe cage. More preferably, the fluid flow entering the cage through oneaperture passes wholly above the adjacent aperture in the same row inthe direction of fluid flow within the cage. This arrangement isparticularly effective when the apertures are arranged in rows withlands therebetween, as in a preferred embodiment of the presentinvention. In this respect, the term ‘above’ is a reference to thelongitudinal direction of fluid flow within the cage in the upstreamdirection. In this way, the fluid flowing within the cage is subjectedto reduced shear within the cage. This is of advantage when the assemblyis being used to process multiphase fluid streams, for examplegas/liquid, liquid/liquid or gas/liquid/liquid fluid streams, where ahigh pressure differential is required between the open and closedpositions of the assembly, for example upstream or downstream of a pump.The reduction in fluid shear within the cage helps to prevent thedifferent fluid phases becoming more highly dispersed. This is ofparticular advantage when the fluid stream is to be subjected to aseparation process downstream of the valve assembly, such as agas/liquid or liquid/liquid separation. This aspect is particularlyadvantageous when processing fluid streams produced from a subterraneanwell, for example gas/oil streams, water/oil streams or gas/water/oilfluid streams, which are to be separated into separate gas, water and/oroil phases.

The cage may comprise apertures of a single size, that is all theapertures have the same cross-sectional area providing the area of theaperture through which the fluid stream flows upon entering the cage.More generally, the cage comprises apertures of a plurality of differentsizes. In such an arrangement, the apertures are preferably arrangedsuch that the apertures first opened when the closure assembly is movedfrom the fully closed position are smaller in size than the aperturesopened subsequently, as the closure assembly moves further to fully openposition.

In one embodiment, the first apertures opened by the closure assembly asit moves from the fully closed position are arranged as described above,that is successive apertures opened are greater in size orcross-sectional area. It has been found that the aperture size can reachan optimum for a given internal diameter of the cage. Once the aperturesopened by the closure assembly have reached this optimum size, it ispreferred that all remaining apertures to be opened have the same,optimum size.

The apertures are preferably of a size and arrangement along the lengthof the cage such that a movement of the closure member in thelongitudinal direction a given distance results in a corresponding givenchange in the volume flowrate of fluid entering the cage.

As noted above, the apertures are preferably arranged in discrete rows,more preferably with a land between adjacent rows of apertures. Each rowmay comprise any suitable number of apertures. The number of aperturesin a given row will depend upon such factors as the size of theapertures required at that position in the wall of the cage, the secondangle of the apertures, and the internal diameter of the cage. Examplesof the number of apertures in a given row in the cage wall are 2, 4, 6or 8. Higher numbers of apertures may be employed, in particular forsmaller size apertures and/or larger cage diameters. In one preferredembodiment, the number of apertures in all the rows of the cage is thesame, with 4 apertures per row being particularly preferred. In analternative preferred embodiment, the first rows of apertures to beopened by the closure member when moving from the fully closed positionhave fewer apertures than the rows to be opened thereafter. For example,the first rows to be opened may have 2 apertures, with the number ofapertures in each row increasing to 4 in successive rows.

The apertures may be arranged in the same position in each row, suchthat a plurality of apertures from different adjacent rows lie on thesame longitudinally extending line of the cage wall. More preferably,the apertures in adjacent rows are staggered or offset in thecircumferential direction from one another, such that apertures inadjacent rows do not lie on the same longitudinally extending line ofthe cage wall.

It has been found that a particularly advantageous flow pattern of fluidwithin the cage is obtained when the apertures in the cage wall arearranged in a helical pattern. The wall of the cage may compriseapertures extending in a single helix or, more preferably in a pluralityof helices from the upstream end of the cage to the downstream end ofthe cage. A particularly preferred arrangement has the aperturesarranged in both rows and in a helical pattern, such that each aperturemay be considered to lie in a row of one or more apertures and a helixof a plurality of apertures.

In one preferred arrangement, the apertures increase in size from thedownstream end of the cage to the upstream end of the cage. Sucharrangements of apertures are discussed above. In this arrangement, eachhelix of apertures comprises a plurality of apertures increasing in sizefrom the downstream end of the cage to the upstream end of the cage.

The helical arrangement of apertures allows for the most efficient useof the wall of the cage. Further, as the closure assembly is movedrelative to the cage, the portion of the closure assembly that iscutting an aperture changes as the position of the closure assemblychanges. This in turn reduces the rate of wear of the closure assembly,by distributing the erosive effect of fluid flow more evenly around theclosure assembly surface.

As noted above, the apertures extend at a first angle through the cagewall and, in a preferred embodiment to a second angle to the radialdirection. In this arrangement, each aperture may be considered tocomprise a leading edge, that is the edge of the aperture that isdownstream in the direction of fluid entering the cage through theaperture, and a lee edge, that is the edge that is upstream of the fluidentering through the aperture.

In one preferred helical arrangement, the apertures in the helix arearranged such their leading edges lie on a single helical line extendingon the interior surface of the cage wall. This arrangement has thebenefit of reducing the shear generated by the fluid streams enteringthe cage on the fluid flowing within the cage. This arrangement isparticularly advantageous when the apertures are comparatively large.

However, it has been found that the above arrangement can provide deadspaces within the cage around the smaller apertures. For comparativelysmall apertures, it is preferred that the apertures in a helix arearranged to have their lee edges lying on a single helical lineextending on the interior surface of the cage wall.

In embodiments in which there is a large difference in the size ofapertures in the cage, for example with small apertures being providedat the downstream end of the cage and significantly larger aperturesbeing provided at the upstream end of the cage, the apertures may bearranged in a helical pattern such that a first group of largerapertures has their leading edges lying on a single helical line and asecond group of smaller apertures has their lee edges lying on a singlehelical line. It is preferred, however, that all the apertures in thecage are arranged in the same manner, that is to have either theirleading edges or their lee edges aligned, as described above.

To direct the flow of fluid within the cage, it is preferred to providea fluid flow guide member. The guide member is preferably formed toreceive the upstream directed fluid leaving the aperture and direct thefluid first radially inwards and then in a downstream direction in theradially central region of the cage interior. In a preferredarrangement, the guide member comprises a guide surface extendinglaterally across the interior of the cage. The radially outer portion ofthe guide surface is provided with a first surface portion extendingradially inwards from the outer edge portion of the guide surface at anangle to the longitudinal axis of the cage in the upstream direction.Suitable angles for the first surface portion are as described above inrespect of the angle of the apertures to the longitudinal axis. In apreferred arrangement, the first surface portion extends atsubstantially the same angle to the longitudinal axis as the apertures.The action of the first surface portion is to guide fluid from theapertures in the upstream direction and radially inwards within thecage.

The guide surface of the guide member preferably comprises a secondsurface portion disposed radially inwards of the first surface portionand centrally within the cage interior. The second surface portion ispreferably provided with a generally rounded profile, such as a roundedcone, having a guide surface extending at an angle to the longitudinalaxis of the cage in the downstream direction. The action of the secondsurface portion is to receive fluid guided by the first surface portionand direct it inwards in the downstream direction. In this way, thefluid entering the cage interior is guided by the fluid guide memberfirst in an upstream direction towards the center of the cage and theninto a downstream flow pattern in the central region of the cageinterior.

In a particularly preferred embodiment, the fluid flow guide member isformed in the end portion of a plug moveable within the cage and forminga closure member, as described below.

As noted above, it is preferred to have the fluid flow in an upstreamdirection within the cage a distance at least the same as the diameterof the fluid flow region within the cage. In embodiments employing aplug, the end portion of the plug may be formed with a longitudinalbore, for example a blind bore, to provide the fluid flow region orchamber through which the fluid flows in the upstream direction. Thelength of this blind bore is preferably at least the same as thediameter of the blind bore. In this arrangement, fluid is caused tocollect within the blind bore in the plug and form a generally staticvolume of fluid, which acts as a hydraulic block. Once this volume ofstatic fluid has formed, it acts to guide the fluid flowing in theupstream direction within the cage, such that the fluid entering thecage through the apertures is caused to flow inwards and changedirection to flow generally downstream in the inner region of the cageby impacting this static fluid. In this respect, the static fluid withinthe blind bore provides a fluid buffer and guide. The fluid buffer andguide may be provided in addition to or as an alternative to the guidemember described above.

The valve assembly of the present invention further comprises a closureassembly. The closure assembly is moveable with respect to the cage toopen and close the apertures in the cage wall by uncovering or coveringthe apertures, respectively. Generally, the cage is fixed within thevalve assembly and the closure assembly is moveable. The closureassembly may comprise a first closure member and/or a second closuremember.

The first closure member, if employed, is disposed within the cage andis moveable with respect to the cage and the apertures extending throughthe wall of the cage. The first closure member acts to open or close theapertures by closing and sealing the inner end of each aperture. Thefirst closure member is moveable between a first or closed position, inwhich it obscures and closes all the apertures in the cage, and a secondor open position, in which it overlies and obscures none of theapertures in the cage. The first closure member may be positionedbetween the first and second positions, such that a portion of theapertures are open for the passage of fluid therethrough, and theremainder of the apertures are closed to the flow of fluid. The flow offluid through the valve assembly may thus be controlled by theappropriate position of the first closure member.

The first closure member may have any suitable form. For example, in thecase of a generally cylindrical tubular cage, the first closure membermay be a cylindrical sleeve or a cylindrical plug, the outer diameter ofwhich corresponds to the inner diameter of the cage.

The first closure member is preferably a plug. The plug has an endsurface that extends across the cage. When the plug is in a positionwith respect to the cage that one or more apertures are open, the endsurface of the plug provides a boundary for a fluid flow path extendingfrom the inlet of the valve assembly, through the open apertures in thecage to the outlet of the valve assembly. The end surface may act toseal the valve by contacting a seat in the valve assembly, when thevalve is closed, with the plug covering all the apertures in the cageand preventing fluid flow through the valve.

The end surface of the plug may be any suitable shape or configuration.If a plug is employed as a closure member, it is preferred to form theend portion of the plug as the fluid guide member within the cageinterior, the features of which are described above.

The second closure member, if employed, is disposed outside the cage andis moveable with respect to the cage and the apertures extending throughthe wall of the cage. The second closure member acts to open or closethe apertures by closing and sealing the outer end of each aperture. Thesecond closure member is moveable between a first position, in which itobscures and closes all the apertures in the cage, and a secondposition, in which it overlies and obscures none of the apertures in thecage. The second closure member may be positioned between the first andsecond positions, such that a portion of the apertures are open for thepassage of fluid therethrough, and the remainder of the apertures areclosed to the flow of fluid. The flow of fluid through the valveassembly may thus be controlled by the appropriate position of thesecond closure member.

The second closure member may have any suitable form. For example, inthe case of a generally cylindrical tubular cage, the second closuremember may be a cylindrical sleeve, the inner diameter of whichcorresponds to the outer diameter of the cage.

The first and second closure members, if both present in the closureassembly, may be moved independently from one another, relative to thecage. In this case, the valve assembly will further comprise an actuatorassembly for each of the first and second closure members. In apreferred arrangement, the first and second closure members are movedtogether, preferably by being connected to one another, by a singleactuator assembly.

Both the first and second closure members may be used to control theflow of fluid through the valve assembly. In one arrangement, the firstand second closure members are sized relative to one another and thecage that, when moved together, at a given position of the closureassembly, the first and second closure members are closing the sameapertures through the cage wall and leaving the same apertures open forfluid flow. In other words, a given aperture will either be open at bothits inner and outer ends or will be closed at both its inner and outerends. In one embodiment, with the apertures formed to have across-section in the form of a parallelogram, the second closure memberonly partially closes the opening of the apertures in the outer wall ofthe cage wall, while the first closure member closes the entire openingon the inner wall surface.

The closure assembly is moved by means of an actuator. Actuator systemssuitable for use in the valve assembly of the present invention areknown in the art and include a range of reciprocating actuator systems.The actuator system may be operated electrically or hydraulically or bya combination of the two. Again, such systems are known in the art. Highpowered actuators may be required to cover the range of pressuredifferentials experienced by the valve assembly, in particular when theassembly is used in subsea environments and is exposed either to highexternal hydrostatic pressures with low internal pressure or highinternal pressure and low external pressure.

The closure assembly may be connected to the actuator system by a shaft.This is particularly advantageous as it allows the actuator moduleitself to be mounted on the exterior of the valve assembly, so that itmay be serviced and or removed without requiring the entire valveassembly to be disassembled. Such an arrangement is also known in theart. The actuator may be arranged to move the shaft longitudinally, suchthat the shaft reciprocates, together with the respective closuremembers. Such an arrangement is well known in the art and suitablereciprocating actuator assemblies are commercially available. In aparticularly preferred arrangement, the closure members are moved by oneor more shafts that transfer drive from the actuator system to theclosure assembly by rotation of the shaft or shafts, as opposed to theconventional reciprocating motion. In the preferred embodiment, with thefirst and second closure members extending from a single support member,a single shaft is required to move the support member and the twoclosure members. The shaft may be connected to the support member in anysuitable way to translate rotational movement of the shaft into internallongitudinal movement of the closure members with respect to the tubularcage. A particularly suitable means for transferring the drive is toprovide a portion of the length of the shaft with a thread that engagesa ball screw nut held captive in the support member.

In operation, the fluid stream to be controlled is introduced through aninlet in the valve assembly. Preferably, the inlet introduces the fluidstream into an annular cavity extending around the outside of the flowcontrol assembly. With the flow control assembly in the fully closedposition, the closure assembly is fully extended with respect to thecage. In this position, all the apertures extending through the wall ofthe cage are covered and closed by the closure assembly, thus preventingfluid from flowing to the outlet of the valve assembly. As the closureassembly is moved with respect to the cage from the closed position, theend surface of each closure member is moved away from its seat. As theend surface of each closure member passes the portion of the cage withapertures therethrough, the apertures are opened and fluid is allowed toflow through the wall of the cage to the outlet of the valve assembly.The extent of fluid flow is controlled by appropriate positioning of theclosure assembly with respect to the cage. As the closure assembly ismoved towards the fully open position, increasing numbers of aperturesare uncovered and the cross-sectional area available for fluid flowincreases.

In practice, it may be difficult to have first and second closuremembers seating at the same time. Accordingly, it may be preferred tohave the first closure member free and not engage a seat, while thesecond closure member is provided with a seat against which it can seal.In this way, the fluid pressure is acting solely to seal the secondclosure member against its seat. This can provide an improved fluidseal.

In general, it is advantageous to employ programmable actuators forvalve assemblies. Programmable actuators allow the pressure and flowrateof the fluid stream to be continuously controlled and adjusted, ensuringthat the pressure/flow system functions accurately within the designlimits. An actuator to move the closure assembly both rapidly andaccurately will allow the process hardware to be designed andconstructed with higher tolerances and with less float or fluctuationtolerance volume, allowing the separation hardware to be more compact.

The present invention has been described in terms of a complete valveassembly. However, it will be appreciated that the particulararrangement of the cage of the valve assembly may be provided as aseparate component, for example for use in repairing or refittingexisting valve assemblies of conventional design.

Accordingly, the present invention further provides a cage assembly foruse in a fluid valve assembly, the cage assembly comprising:

a cage wall having apertures therethrough to provide passage for fluidpassing from the exterior of the cage to the interior of the cagethrough the cage wall, the cage having a longitudinal axis;

wherein the apertures in the cage extend through the cage at a firstangle to the longitudinal axis of the cage, such that, in use, fluidentering the cage through each aperture is directed into the cage at anangle to the longitudinal axis in an upstream direction.

As described above, the apertures in the cage preferably extend throughthe cage wall at a second angle to the radial direction.

Features of the cage and, in particular, the apertures in the cage wall,are as hereinbefore described.

The valve assembly of the present invention finds use generally in thecontrol of fluid streams, in particular the control and regulation ofthe fluid pressure or flowrate. The valve assembly finds particular usein the control of fluid streams produced from subterranean wells, inparticular multiphase fluid streams, for example comprising two or moreof oil, water, gas and entrained solids.

Accordingly, there is also provided a wellhead assembly for asubterranean well comprising a valve assembly as hereinbefore described.

Referring to FIG. 1, there is shown a valve assembly, generallyindicated as 2, according to a first embodiment of the presentinvention. The valve assembly 2 comprises a generally cylindrical lowerhousing 4 and a generally cylindrical upper housing 6. The upper housing6 has a flange 8 formed around its lower end portion, allowing the upperhousing 6 to be mounted to the lower housing 4 by means of bolts 10 in aconventional manner.

References herein to ‘upper’ and ‘lower’ are used for the purposes ofease of identification of components in the accompanying figures and areused in relation to the orientation of the apparatus shown in thefigures only, it being understood that the assemblies of the presentinvention may be used in any appropriate orientation and need not belimited to operation in the orientation shown in the accompanyingdrawings.

The lower housing 4 comprises a generally cylindrical flow chamber 12formed therein and has an inlet 14 for fluid and an outlet 16 for fluid.The inlet 14 has a generally circular cross-section in its upstreamportion, with a smooth transition portion to a generally rectangularfeed section in its downstream portion immediately before the openinginto the flow chamber 12. The inlet 14 is arranged laterally to open inthe side of the flow chamber 12, as shown in FIG. 1, while the outlet 16is arranged axially in the lower portion of the lower housing 4, as alsoshown in FIG. 1. Fluid to be processed by the valve assembly 2 is led tothe inlet 14 by a conventional pipe (not shown for clarity). Theprocessed fluid is led away from the outlet 16 through a conventionalpipe 18, mounted to the lower portion of the lower housing by means of aflange 20 and bolts 22, again of conventional design.

The upper housing 6 comprises a first, generally cylindrical chamber 24therein in its lower region which opens into the flow chamber 12 in thelower housing 4. The upper housing 6 further comprises a second,generally cylindrical chamber 26 therein in its upper region. The secondchamber 26 is sealed from the first chamber as described hereinafter. Anactuator assembly 30, of known design and commercially available, ismounted to the upper end of the upper housing 6 by bolts 32, inconventional manner. The actuator assembly 30 may comprise any suitableform of actuator, for example a hydraulic, electro-hydraulic or electricactuator. Electric actuators are preferred.

The valve assembly 2 further comprises a flow control assembly,generally indicated as 34, disposed within the flow chamber 12 of thelower housing, the flow control assembly 34 having a closure assembly,generally indicated as 36. Components of the closure assembly 36 extendinto the first chamber 24 in the upper housing 6 and into the secondchamber 26 of the upper housing 6. The closure assembly 36 is sealed tothe interior of the upper housing 6 at the junction between the firstand second chambers 24, 26. Details of the flow control assembly and theclosure assembly are described hereinafter.

A shaft 38 extends from the actuator assembly 30 and connects with theupper end of the closure assembly 36, further details and the operationof which are provided herein below.

As noted above, the fluid inlet 14 to the flow chamber 12 of the lowerhousing 4 is disposed in the side of the lower housing, so as to directincoming fluid laterally into the flow chamber 12. Referring to FIG. 2,there is shown a cut-away cross-sectional view of the lower housing 4,with a portion of the flow control assembly 34 removed, to show detailsof the fluid inlet arrangement of the flow chamber 12. A diagrammaticalcross-sectional view along the line III-III of FIG. 2 is shown in FIG.3.

Referring to FIG. 2, the inlet 14 is arranged to have an inlet passage40 extending tangentially into the flow chamber 12. The inlet 14 isformed to provide the inlet passage 40 with a generally circular feedportion 42, and a generally rectangular orifice 44, indicated by adotted line, opening into the flow chamber 12. The inlet passage 40 isarranged to open at the orifice 44 tangentially to the inner wall of thelower housing 12. In this way, fluid entering the flow chamber 12through the inlet passage is caused to flow in a circular pattern withinthe flow chamber 12. This has the effect of distributing the fluidaround the flow control assembly 34 within the flow chamber 12. This hasa number of advantageous effects. First, the incoming fluid is notcaused to directly impinge upon the outer surfaces of the flow controlassembly 34, as is the case with known and conventional plug-and-cagechoke designs. This in turn prevents damage to the flow control assembly34 arising from the impact of entrained solid materials and particles.Second, introducing the fluid into the flow chamber 12 tangentiallyallows the fluid to flow in a lower shear regime that is possible withthe conventional and known arrangements, in which the incoming fluid isdirected orthogonally at the plug-and-cage assembly. This in turnreduces the effects to which the various phases in the fluid stream aremixed, perhaps undoing earlier separation that may have occurred in theprocess lines and equipment upstream of the valve assembly. Further, thecircular or rotating flow pattern within the flow chamber 12 inducesseparation of the different phases within the fluid stream, according tothe respective densities of the phases. Further, the arrangement shownin the figures ensures that the incoming fluid stream is evenlydistributed within the flow chamber 12 around the flow control assembly.This in turn increases the effectiveness and efficiency of the flowcontrol assembly in controlling the flowrate and/or pressure of thefluid stream.

The inner wall of the lower housing 4 defining the flow chamber 12 isformed with a channel 46 therein. The channel 46 is aligned with theorifice 44 and forms an involute path for fluid entering the flowchamber 12. The channel 46 is extends circumferentially around the flowchamber 12, as shown in FIG. 3. The channel 46 decreases incross-sectional area, travelling in the circumferential direction awayfrom the orifice 44, that is the path followed by the incoming fluidstream. In this way, the fluid stream is encouraged gradually to enterthe central region of the flow chamber 12 and flow towards the centrallylocated flow control assembly 34.

Details of the cross section of the channel 46 are shown in FIGS. 4a,4b, 4c and 4d at the positions A, B, C and D of FIG. 3, respectively. Ascan be seen, the cross-sectional area of the channel 46 decreases in thedirection of fluid flow circumferentially away from the inlet orifice44. This reduction in cross-sectional area of the channel 46 ensuresthat fluid leaves the channel as it travel circumferentially around theflow chamber 12, as noted above. This reduction in cross-sectional isachieved in the embodiment shown in FIGS. 2 and 3 by having the depth ofthe channel 46 decrease in the direction extending circumferentiallyaway from the orifice 44. However, in the embodiment shown, thisreduction in depth is accompanied by an increase in the width of thechannel in the longitudinal direction of the lower housing 12. Thisincrease in width has the effect of distributing the fluid streamlongitudinally within the flow chamber 12. This in turn ensures that theflow control assembly has an even exposure to the fluid stream to becontrolled. The reduction in cross-sectional area of the channel 46 ispreferably gradual or progressive, as shown in FIGS. 2 and 3. In theembodiment shown, the cross-sectional area reduces by 25% for each 90°of turn of the fluid stream. Thus, if the cross-sectional area of theorifice 44, as shown in FIG. 4a is A, the cross-sectional area of thechannel at the positions shown in FIGS. 4b, 4c and 4d is 0.75A, 0.5A and0.25A, respectively.

Referring to FIG. 5, there is shown a vertical cross-sectional view ofthe lower housing 4 of the valve assembly 2 of FIG. 1, showing the flowcontrol assembly 34. The flow control assembly 34 comprises a cage 50formed as a generally cylindrical tube extending longitudinally withinthe flow chamber 12. The cage 50 has a plurality of apertures 52extending therethrough, details of which are described herein below. Thecage 50 has its lower end portion formed with a thread 54 on its outersurface. The cage 50 is mounted within the flow chamber 12 by beingscrewed into a threaded boss 56 inserted into the lower end wall of thelower housing 12 adjacent the fluid outlet 16. The interior of the cage50 is in fluid flow communication with the fluid outlet 16 by means of abore formed in the boss 56, such that fluid flowing through theapertures 52 in the cage 50 and entering the interior of the cage 50 mayleave the valve assembly through the outlet 16.

The flow control assembly 34 further comprises a closure assembly 36.The closure assembly 36 comprises a plug 60 extending within the centralbore of the cage 50. The plug 60 is machined to be a close fit with theinner walls of the cage 50 and is slideable longitudinally within thecage 50, as will be described hereinafter. The plug 60 is generallycylindrical, having a longitudinal bore 62 formed therein. The bore 62is open to the interior of the cage 50 by virtue of a small diameterbore 64 formed in the end of the plug 60. In this way, fluid within thebore 62 is able to leave the plug 60, thus preventing a hydraulic lockoccurring.

A plurality of balancing bores 66 extending longitudinally through theplug 60. Each balancing bore 66 opens into the interior of the cage 50.The balancing bores 66 are features of the fluid balancing system in thevalve assembly, details of which are described herein below.

The plug 60 is shown in the fully closed position in FIGS. 1 and 5, thatis the plug 60 extends within the cage 50 and covers or obscures theinner ends of all the apertures 52 in the cage 50. It will be noted thatthe lower or free end of the plug 60 extends within the boss 56, that isa significant distance past the lowest apertures 52 in the cage 50.

The plug 60 depends at its upper end from the lower end of a generallycylindrical piston 68. The piston 68 extends upwards from the top of thecage 50, through the first chamber 24 in the upper housing 6 and intothe second chamber 26, as shown in FIG. 1. The non-rotatable piston 68engages with grooves in the wall of the first chamber and is moveablelongitudinally within the upper housing 6, that is vertically as shownin FIG. 1, in association with the plug 60. Seals 70 are disposed in theinner wall of the upper housing 6 at the junction between the firstchamber 24 and the second chamber 26. The seals 70, of conventional orknown configuration, allow the longitudinal movement of the piston 68within the first and second chambers, but prevent fluid from passingbetween the first and second chambers 24, 26. The piston 68 has acentral longitudinal bore 72, communicating with the bore 62 in the plug60 at its lower end and opening into the second chamber 26 at its upperend, to receive the shaft 38. A plurality of fluid balancing bores 74extend longitudinally within the piston 68, the lower end of eachbalancing bore 74 communicating with a corresponding balancing bore 66in the plug 60, and the upper end of each fluid balancing bore 74opening into the second chamber 26 within the upper housing 6.

The closure assembly 36 further comprises a sleeve assembly 80. Thesleeve assembly 80 is generally cylindrical and extends from the lowerend of the piston 68 around and along the outer surface of the cage 50such that the sleeve assembly 80 can obscure and cover the outer ends ofthe apertures 52 in the cage. The sleeve assembly 80 is formed to be aclose fit around the exterior surface of the cage 50, while stillallowing the sleeve assembly 80 to move longitudinally with respect tothe cage 50. The sleeve assembly 80 comprises an inner sleeve 82 and anouter sleeve 84, both generally cylindrical in form. The outer sleeve 84is unitary with the piston 68. The inner sleeve 82 extends within theouter sleeve and is retained by a connection 86 at their respectivelower ends. This arrangement allows the inner sleeve 82 to be formedfrom a first material, such as tungsten, and the outer sleeve form froma second material, such as stainless steel.

By being attached to the piston 68, the sleeve assembly is moveable bothwith the piston 68 and the plug 60. In particular, the sleeve assembly80 moves together with the plug 60 under the action of the actuatorassembly 30. The control of the flow of fluid through the apertures 52of the cage 50 is determined by the positions of the plug 60 and sleeveassembly 80 with respect to the cage. As shown in the figures, the plug60 extends a greater distance from the end of the piston 68 than thesleeve assembly 80. This arrangement in turn provides the plug 60 andthe sleeve assembly 80 with different functions. In particular, in thearrangement shown, the sleeve assembly 80 primarily acts as a flowshut-off member, that is to ensure that the flow of fluid is prevented,when the assembly is in the fully closed position, as shown in FIG. 5,for example. When the assembly has been moved from the fully closedposition shown, the control of the flow of fluid through the cage 50,and hence through the entire assembly, is primarily controlled by theplug 60.

In order to perform the function of a flow shut-off member, that isprevent the flow of fluid through the assembly, the sleeve assembly 80is provided with a sealing arrangement at its lower end, that is the enddistal of the piston 68. Referring to FIG. 6, there is shown an enlargedview of a portion of the flow control assembly 34 of FIG. 1, inparticular showing the lower or distal end of the sleeve assembly 80. Aseating ring 90 is mounted in the boss 56 by a threaded connection 92and extends around the cage 50. The seating ring 90 is formed from aseating material, to allow a ridge on the closure member to bed in. Aseating surface 94 is formed by the surfaces of the boss 56 and theseating ring 90 exposed within the flow chamber 12. As can be seen inFIG. 6, the seating surface 94 extends at an angle to the radialdirection, such that it slopes away from the free end of the sleeveassembly 80. The action of the angled seating surface is twofold. First,by being angled, debris is prevented from collecting on the seatingsurface and stopped from preventing a fluid-tight seal being formedbetween the sleeve assembly 80 and the seating surface. Rather, solidparticles and debris are collected in the lower region of the flowchamber 12, as viewed in FIG. 6, around the base of the cage. Second,the angle of the seating surface 94 cooperates with the surfaces on theend of the sleeve assembly 80 to be self-sharpening, as is describedherein below.

The seating surface 94 cooperates with the end portion of the sleeveassembly 80. As shown in FIG. 6, the free or distal end of the outersleeve 84 is finished perpendicular to the longitudinal axis of thesleeve assembly, plug and cage. The distal end of the inner sleeve 82 isformed with a compound surface comprising a first surface portion 96radially outwards of a second surface portion 98. The first surfaceportion 96 extends at an angle to the radial direction that is moreacute than the angle of the seating surface 94. The second surfaceportion 98 extends at an angle to the radial direction that is moreobtuse than the angle of the seating surface 94. The first and secondsurface portions 96, 98 meet at a ridge 100. The details of the seatingsurface 94 and its cooperation with the surfaces at the distal end ofthe sleeve assembly 80 are shown in FIG. 7.

In operation, the ridge 100 is forced by the actuator assembly 30 intocontact with the seating surface 94 of the seating ring 90, as the flowcontrol assembly is moved into the fully closed position, shown in FIGS.6 and 7. Contact between the ridge 100 and the seating surface 94 formsa fluid-tight seal. Depending upon the force exerted by the actuatorassembly 30, the ridge 100 is caused to slide along the seating surface94, due to the angle of the seating surface 94. This sliding actioncauses the ridge 100 and seating surface 94 to bed in, in particular towear and removes pits, marks and blemishes in the surfaces, which mayprevent a proper fluid seal from being formed. In addition, the actionof the actuator assembly 30 moving the sleeve assembly 80 in thelongitudinally downwards direction, as viewed in FIGS. 6 and 7, resultsin a force being exerted on the ridge 100 and the distal end of thesleeve assembly 80 by the seating surface 94, as indicated by arrow P inFIG. 7. This force, normal to the seating surface 94, has a radiallyoutwards component, which induces a hoop stress in the distal endportion of the sleeve assembly 80. The action of the hoop stress is toforce the ridge 100 radially inwards, against the seating surface 94, asindicated by arrows Q in FIG. 7. This in turn increases theeffectiveness of the seal formed between the ridge 100 and the seatingsurface 94. In particular, high hoop stresses can be generated, in turncausing the ridge 100 to bed into the seating surface 94.

As noted above, the plug 60 and sleeve assembly 80 extend differentlongitudinal distances from the piston 68 and with respect to the cage50. The closure assembly 36 is moveable between a fully closed position,as shown in FIG. 6, for example, to a fully open position. In the fullyclosed position, the sleeve assembly 80 is sealed against the seatingsurface 94, as described above and shown in detail in FIG. 7. The plug60 extends longitudinally within the cage 50, with its free endextending beyond the seating surface 94, as shown in FIG. 6. In thefully closed position, the plug 60 and the sleeve assembly 80 cover andobscure the inner and outer ends of the apertures 52 in the cage 50,respectively, thus preventing fluid flow through the assembly 2. Withthe closure assembly in the fully open position, both the inner andouter ends of all the apertures 52 in the cage 50 are uncovered andopen, allowing maximum fluid flow through the assembly. With the closureassembly 36 in an intermediate position, the flow of fluid is controlledbetween the maximum flow and zero.

As noted, the sleeve assembly 80 has the primary function of shuttingoff fluid flow, by sealing against the seating surface 94, when in thefully closed position. As the actuator assembly 30 moves the closureassembly 36 longitudinally from the fully closed position, the sleeveassembly 80 is lifted from the seating surface 94, as shown in FIG. 8.The sleeve assembly 80 is moved to expose the outer ends of theapertures 52 closest to the seating surface 94. However, the plug 60,extending longitudinally further than the sleeve assembly 80, stillcovers the inner ends of all the apertures 52 in the cage 50. As aresult, fluid does not flow. Rather, further movement of the closureassembly 36 beyond the position shown in FIG. 8 is required, such thatthe inner ends of apertures 52 are exposed and the respective aperturesfully opened to allow fluid to flow therethrough. It will thus beappreciated that, once the closure assembly 36 is moved from the fullyclosed position of FIG. 6, the control of fluid flow is achieved by theposition of the plug 60 with respect to the cage 50. This arrangementprevents the fluid flow causing erosion of the seat 94 and the ridge100, regardless of the position of the sleeve assembly 80.

The arrangement of the closure assembly 36 comprising both a sleeveassembly 80 and a plug 60, as described above, is a particularlyadvantageous arrangement. However, it will be appreciated that the cage50 of the present invention may be used with this arrangement havingboth a sleeve assembly and a plug or with a closure assembly having justone of the sleeve assembly or the plug.

Referring to FIG. 9, there is shown a detailed cross-sectional view ofthe actuator mechanism, in particular the connection between theactuator assembly 30 and the shaft 38. The actuator assembly 30comprises an electric motor and gear drive assembly of conventionaldesign (not shown for clarity). A torque shaft 110 extends from theactuator assembly 30 longitudinally through the end of the upper housing6. The torque shaft 110 is connected to the upper end of the shaft 38,as viewed in FIG. 9 by a key and slot arrangement 112. In operation, thetorque shaft 110 is rotated by the electric motor and gear assembly, therotation of which is transferred directly to the shaft 38. Abi-directional thrust bearing assembly 114 is disposed in the end of theupper housing 6 and supports the torque shaft. A seal 116 ofconventional design is provided in the end of the upper housing aroundthe end portion of the shaft 38, to provide a seal against fluid leakingfrom the upper chamber 26 of the upper housing 6. In addition, inoperation, hydraulic transmission fluid is supplied to the thrustbearing assembly 114 through a port 118 extending through the housing 6and provides hydraulic compensation against the pressure of the fluid inthe upper chamber 26 of the upper housing 6. The pressure of thehydraulic transmission fluid may be slightly higher than the fluidpressure within the upper housing 6. This arrangement means that theseal 116 is only required to provide a separation action between thepressure of the fluid within the valve assembly and the hydraulictransmission fluid, in turn increasing the working life andeffectiveness of the seal 116.

The end portion of the shaft 38 distal from the actuator assembly 30(that is the lower end as viewed in the figures) extends into the piston68, as shown in FIG. 10. The piston 68 of the closure assembly 36comprises a longitudinal bore 120, within which is mounted a generallytubular insert 122 having a central bore 124, by means of a threadedconnection 126. The central bore 124 of the insert 122 aligns with thecentral bore 62 within the plug 60. The shaft 38 extends longitudinallywithin the insert 122, a portion 130 of the shaft extending within theinsert being provided with a thread on its outer surface. The insert 122retains within the bore 120 of the piston 68 a ball screw nut 132 toengage with the threaded portion 130 of the shaft 38. Rotation of theshaft 38, by means of the actuator assembly 30, is translated intolongitudinal movement of the piston 68 by the engagement between thethreaded portion 130 of the shaft and the ball screw nut 132.

The shaft 68 and insert 122 are provided with seals 134 and 136,respectively, to prevent fluid ingress from the open, upper end of thepiston, as shown in FIG. 10. The free or distal end of the shaft 38 isprovided with a sealing cap 138, connected to the endmost portion of theshaft 38 by a threaded connection. The sealing cap 138 is provided withfluid seals 140, to bear against the wall of the bore 62 in the plug 60.In operation, the sealing cap 138 is caused to rotate within the bore 62in the plug 60, as the piston 68 is caused to move longitudinally byrotation of the shaft 38, as hereinbefore described.

As noted above, the cage 50 is provided with a plurality of apertures 52therethrough, to allow fluid to flow from the flow chamber 12 to theoutlet 16. The apertures 52 may be of conventional distribution in thewall of the cage.

Conventional designs employ circular apertures extending perpendicularto the outer surface of the cage in the radial direction, that is extendradially inwards. The apertures are nested to have the apertures in onerow extend into the interstices between the apertures of each adjacentrow. In this way, the sleeve or plug moving along the outer or innersurface of the cage is varying the area of exposed apertures throughoutits entire movement. This has the advantage of allowing a compact cageto be formed and use a plug or sleeve having a short stroke. However,this has been found to cause a very rapid and deleterious erosion of theend surfaces and portions of the plug or sleeve.

In general, the arrangement of the apertures is such that the curvatureof the inner wall of the cage 50 is accommodated by the shape of thecross-section of the apertures, such that the opening of each apertureat the inner wall of the cage 50 is rectangular, giving rise to arectangular jet of fluid entering the interior of the cage in use. Aswill be described below, this is achieved by providing the apertureswith a rhombic cross-section.

Referring to FIG. 11, there is shown a vertical cross-sectional view ofa portion of a cage 50 of preferred configuration, together with thelower end portion of the sleeve and plug of the closure assembly. Asshown in FIG. 11, the cage 50 comprises a plurality of apertures 52extending through the wall of the cage, each aperture having an openingin both the inner and outer surface of the cage wall. FIG. 12 shows ahorizontal cross-section through the cage 50 of FIG. 11, showing a rowof apertures. Each aperture extends at both an angle to the radialdirection and at an angle in the longitudinal direction to the normal orperpendicular, as will now be described.

Referring to FIG. 11, the general direction of fluid flow through thebore of the cage 50 when in use is represented by arrow H. This generaldirection is longitudinally within the cage 50 and is generallydownwards, as viewed in FIG. 11. Considering the angle of the aperturesto the vertical plane, as shown in FIG. 11, each aperture extendsthrough the wall of the cage from the outer surface to the inner surfaceat an angle to the longitudinal axis in the upstream direction of flow,that is the opposite direction to that indicated by the arrow H. In thisway, fluid entering the cage is directed initially by the apertures inthe upstream direction. The apertures may extend at any suitable angleto the longitudinal axis and the angle will depend upon such factors asthe dimensions of the cage and valve assembly, and the nature andcomposition of the fluid being processed.

In the arrangement shown in the figures, the apertures extend at anangle β to the longitudinal axis of 65°. The angle of the apertures mayrange from 40° to 85°, more preferably from 50° to 80°. It is preferredthat the apertures are angled in the longitudinal direction sufficientto ensure that the jet of fluid entering the cage through one apertureand flowing in a circular pattern adjacent the inner wall of the cageavoids contacting the jet of fluid entering the cage through theadjacent aperture in the direction of travel of the fluid.

Considering the second angle of the apertures, that is the angle to theradial direction in the plane perpendicular to the longitudinal axis,each aperture 52 extends through the wall of the cage 50 at an angle tothe radial direction and opens tangentially to the inner wall of thecage 50. In operation, this causes the fluid to enter the cage 50flowing in a direction parallel to the inner wall and to flow in acircular pattern, as represented in FIG. 12. This circular flow patternprevents the incoming jets of fluid from opposing apertures fromcolliding within the cage. This in turn helps to maintain any separationof fluid phases that may be occurred or been induced upstream of thevalve assembly and reduces the burden on fluid separation apparatusdownstream of the assembly.

Further, in operation, the arrangement of the apertures 52 induces thefluid to flow upon entering the cage in a helical pattern within thecage in the general upstream direction within the interior of the cage,that is in the opposite direction to the arrow H, with the fluid beingsubjected to minimal shear.

The apertures 52 are arranged in discrete rows extendingcircumferentially around the cage, each row containing one or moreapertures, more preferably at least two apertures. The rows areseparated by portions of the cage wall having no apertures, or ‘lands’150. This allows the plug 60 to be positioned such that its end surfacedoes not extend across the inner opening of one or more apertures 52. Inthis way, the fluid entering the cage 50 through the open apertures 52adjacent the end of the plug 60 is not caused to flow or cut across theend surface of the plug 60, in turn reducing the erosion of the plug 60by the fluid stream.

The apertures 52 in the cage 50 vary in cross-sectional area availablefor fluid flow as shown, such that the apertures in the rows closest tothe fluid outlet (that is the lower portion of the cage 50 as shown inthe figures) have the smallest cross-sectional area available for fluidflow, with the area for fluid flow increasing in the reverse directionof general fluid flow H or up the cage as shown in the figures. The rowsof apertures are grouped according to aperture size, with each groupcomprising two, three or more rows of apertures of a givencross-sectional area.

The cross-section of each aperture is rhomboidal in shape, rather thanrectangular, with the upper and lower edges of the rhomboid, as viewedin FIG. 11, being curved. This correction to the shape of the apertureshas been found to be useful in minimizing the width of the landsrequired between adjacent rows of apertures, in turn reducing theoverall length of the cage and closure assembly.

The assembly comprises a flow guide within the interior of the cage 50.In the embodiment shown in FIG. 11, the flow guide is formed on thelower end of the plug 60 and is generally indicated as 300. The flowguide 300 is integrally formed in the lower end portion of the plug 60.As an alternative, the flow guide may be formed as a separate componentand attached to the end portion of the plug 60.

The flow guide 300 comprises a radially outer portion 302 extendingupwards and inwards from the radially outer edge 60 a of the plug 60. Inthe embodiment shown in FIG. 11, the outer portion 302 extends at thesame angle β to the longitudinal axis as the apertures 52. The flowguide 300 further comprises a radially inner portion 304 which extendsdownwards from the end surface of the plug and is generally of curvedfrusto-conical form. The outer edge 60 a of the plug is radiused, asshown in FIG. 11.

In operation, fluid enters the interior of the cage 50 through theapertures 52 and is directed in an upstream direction, that is upwardsin FIG. 11. The outer portion 302 of the flow guide 300 acts to directthe fluid flow upwards and inwards towards the center of the cage 50. Asthe fluid contacts the inner portion 304 of the flow guide 300, it isdiverted to flow in the downstream direction, that is in the directionof arrow H in FIG. 11. The overall arrangement provides a fluid flowpattern that has fluid flowing generally upstream in the radially outerregion of the cage interior and flowing generally downstream in theradially inner or central region of the cage interior.

As described hereinbefore, the closure assembly 36 is provided withbores 66 and 74 extending through the plug 60 and piston 68respectively. These bores are provided to allow the closure assembly 36to be balanced with respect to the fluid pressure at the outlet. Theprinciples of this pressure balancing will now be described havingreference to FIG. 1.

Referring to FIG. 1, as described above, the plug 60 and sleeve assembly80 both depend from the piston 68 of the closure assembly 36. The sleeveassembly 80 is moveable longitudinally within the first chamber 24 inthe upper housing 6 of the assembly 2. However, the sleeve assembly isnot sealed within the first chamber 24. Rather, fluid is allowed to flowfrom the flow chamber 12 into the first chamber 24 past the sleeveassembly 80, which fluid is at the fluid inlet pressure. A shoulder 200is formed at the junction between the sleeve assembly 80 and the piston68.

The shoulder 200 is exposed to fluid within the first chamber 24. Fluidpressure within the first chamber 24 thus bears on the surface of theshoulder 200 and acts to move the sleeve assembly 80 and the entireclosure assembly 36 in the longitudinally downwards direction, as viewedin FIG. 1. Fluid at the inlet pressure within the flow chamber 12 alsobears on the free or distal end surfaces of the sleeve assembly 80,urging the sleeve assembly 80 and the entire closure assembly 36longitudinally upwards, as viewed in FIG. 1. The net force acting on thesleeve assembly 80 and urging the closure assembly 36 and its directiondepends upon the ratio of the surface area of the shoulder 200 withinthe first chamber 24 and the surface area of the end surfaces of thesleeve assembly 80 within the flow chamber 12. The balancing of theclosure assembly with respect to the inlet fluid pressure may thus beachieved by appropriate sizing of the shoulder 200 with respect to theend surface of the sleeve assembly 80. The arrangement allows for thissizing to be achieved by varying the diameter of the piston 68.

The sleeve assembly 80 has an inner diameter Ds shown in FIG. 1.Similarly, the piston 68 has an outer diameter Dp shown in FIG. 1. Inthe arrangement that Dp is less than Ds, the surface area of theshoulder 200 within the first chamber 24 is greater than the surfacearea of the end surface of the sleeve assembly 80. In such a case, theclosure assembly 36 is biased into the fully closed position by theinlet fluid pressure. Similarly, with Dp greater than Ds, the surfacearea of the shoulder 200 is less than the area of the free end surfaceof the sleeve assembly 80, thus having the closure assembly biased intothe fully open position by the inlet fluid pressure. With Dp equal toDs, the closure assembly is neutrally biased or balanced with respect tothe inlet fluid pressure.

As described above, ports 66 and 74 ensure that the second chamber 26 inthe upper housing 6 is in fluid communication with fluid within the cage50, that is fluid at the outlet pressure. Fluid pressure in the secondchamber 26 bears on the upper or exposed end of the piston 68, giving aneffective area of Dp less the area of the shaft 38, urging the pistonand closure assembly longitudinally downwards, as viewed in FIG. 1, intothe fully closed position. Fluid within the cage 50 bears upon theexposed or distal end surface of the plug 60 and inner area giving atotal effective area of Ds less the area of the end of the shaft 38,urging the plug and closure assembly 36 longitudinally upwards, asviewed in FIG. 1. The net force acting on the closure assembly 36 by thefluid at outlet pressure and its direction is determined by the ratio ofthe surface areas of the free end of the piston 38 and the distal end ofthe plug 60. In the arrangement shown, the net effect of the fluid atthe outlet pressure acting within the cage 50 and within the secondchamber 26 is to neutrally bias or balance the closure assembly 36 withrespect to the outlet pressure.

The assembly of FIG. 1 may be arranged to have the closure assembly 36during operation balanced by the fluid pressures such that there are nonet forces acting to urge the closure assembly 36 into either the fullyopen or fully closed position. In this arrangement, the actuatorassembly 30 is required to perform the least work to move the closureassembly and operate the valve assembly. Alternatively, the closureassembly may be sized to have the net fluid pressure bias the closureassembly into the fully open or fully closed position. Thus, theassembly may be termed as open- or closed-friendly, as required, that iswith the biasing assisting the actuator in opening or closing the valve.While this may be preferred and required for certain operations, thebiasing applied to the closure assembly by the fluid pressures will needto be overcome by the actuator assembly, during operation. This willlikely increase the load on the actuator assembly and, in the case ofhigh pressure fluids, require a more powerful actuator assembly to beemployed.

Turning to FIG. 13, there is shown a cross-sectional view of a plug andcage assembly according to an embodiment of the present invention. Theplug and cage assembly is generally indicated as 402 and comprises agenerally cylindrical cage 404 having apertures 406 extendingtherethrough. The configuration and arrangement of the apertures 406 maybe as described above.

A moveable closure assembly comprises a generally cylindrical plug 408moveable axially within the cage 404. With the plug 408 in the positionshown in FIG. 13, the apertures 406 in the cage 404 are all fullyuncovered and is the full flow position for the plug. Movement of theplug 408 in a downwards direction, as viewed in FIG. 13, progressivelycloses the apertures 406, thereby reducing the flow of fluid through theapertures into the cage interior. The plug 408 is provided with a blindbore 410 formed in its end portion. The blind bore 410 forms a cavityhaving a diameter D, as indicated in FIG. 13, and a length D, alsoindicated in the figure.

In the arrangement of FIG. 13, fluid being processed has a generaldownstream direction of flow towards the outlet of the assembly (notshown in FIG. 13 for clarity) as indicated by the arrow A, that isdownwards as viewed in FIG. 13.

In operation, fluid enters the interior of the cage 404 through theapertures 406. The apertures 406 are formed to extend through the wallof the cage tangentially to the inner surface of the cage and in anupwards direction, as viewed in FIG. 13. As a result, the fluid enteringthe cage 404 is caused to flow upwards as viewed in FIG. 13, that is inan upstream direction and in a helical flowpath in the radially outerregion of the cage interior. This upwards helical flowpath is indicatedas H1 in FIG. 13. The flowpath H1 extends into the end portion of thebore 410, as shown. The remaining volume within the bore 410 is filledwith generally static fluid, causing a hydraulic block. Following theupstream flowpath H1, the fluid encounters the static fluid within thebore 410, causing the fluid to change direction and follow a generallyhelical downstream flowpath H2, in the radially inner or central regionof the cage interior.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

The techniques presented and claimed herein are referenced and appliedto material objects and concrete examples of a practical nature thatdemonstrably improve the present technical field and, as such, are notabstract, intangible or purely theoretical. Further, if any claimsappended to the end of this specification contain one or more elementsdesignated as “means for [perform]ing [a function] . . . ” or “step for[perform]ing [a function] . . . ”, it is intended that such elements areto be interpreted under 35 U.S.C. 112(f). However, for any claimscontaining elements designated in any other manner, it is intended thatsuch elements are not to be interpreted under 35 U.S.C. 112(f).

The invention claimed is:
 1. A valve assembly comprising: a valve housing; an inlet for fluid entering the valve housing; an outlet for fluid leaving the valve housing; a flow control assembly disposed within the valve housing between the inlet and the outlet, whereby fluid entering the valve housing is caused to flow through the flow control assembly, the flow control assembly comprising: a cage having apertures therethrough to provide passage for fluid passing from the inlet to the outlet, the cage having a longitudinal axis and an outlet end, in use fluid generally flowing within the cage in a downstream direction towards the outlet end; a plug with a flow guide member, wherein the flow guide member comprises a guide surface extending laterally across an interior of the cage, wherein a radially outer portion of the flow guide member is provided with a first curvilinear circumferential surface portion extending at second angles tangent thereto, wherein the second angles extend in an upstream direction with respect to the longitudinal axis of the cage, a radially inner portion of the flow guide member is provided with a second curvilinear surface portion extending at third angles tangent thereto, wherein the third angles extend in the downstream direction with respect to the longitudinal axis of the cage to redirect the fluid flowing over the first curvilinear surface portion in the downstream direction, wherein the second curvilinear surface portion is a rounded cone.
 2. The valve assembly according to claim 1, wherein all the fluid entering the valve housing through the inlet is caused to flow through the flow control assembly to the outlet.
 3. The valve assembly according to claim 1, wherein the valve housing comprises a cavity therein, the flow control assembly being disposed within the cavity, such that the cavity extends around the flow control assembly.
 4. The valve assembly according to claim 3, wherein the inlet extends at an angle to a radial direction within the cavity, such that fluid entering the cavity is not caused to impinge directly onto the flow control assembly.
 5. The valve assembly according to claim 4, wherein the inlet is tangential to a wall that defines the cavity, and wherein fluid enters the cavity along the wall that defines the cavity.
 6. The valve assembly according to claim 5, wherein the wall defines an involute channel that extends circumferentially around the flow control assembly, and wherein the inlet is configured to direct an incoming fluid stream into the involute channel.
 7. The valve assembly according to claim 6, wherein the involute channel has a progressively smaller cross-sectional area travelling in a direction of flow of fluid in the channel.
 8. The valve assembly according to claim 1, wherein the apertures are arranged in the cage in a plurality of rows, each row containing at least one aperture, adjacent rows being separated by a land having no apertures therethrough.
 9. The valve assembly according to claim 8, wherein the adjacent apertures in adjacent rows are offset circumferentially from one another around an exterior of the cage, wherein the adjacent apertures in adjacent rows extend in a helical pattern along and around the cage.
 10. The valve assembly according to claim 1, wherein the apertures in the cage extend through the cage at an angle less than 85° with respect to the longitudinal axis of the cage.
 11. The valve assembly according to claim 10, wherein the apertures in the cage extend through the cage at an angle less than 80° with respect to the longitudinal axis of the cage.
 12. The valve assembly according to claim 10, wherein the apertures in the cage extend through the cage at an angle from 50° to 80° with respect to the longitudinal axis of the cage.
 13. The valve assembly according to claim 1, wherein the apertures extend through a wall of the cage at a second angle being an angle to a radial direction of the cage.
 14. The valve assembly according to claim 13, wherein a first aperture is angled to guide fluid entering an interior of the cage through the first aperture to pass above a stream of fluid entering the cage through a second aperture adjacent the first aperture in the same lateral plane as the first aperture.
 15. The valve assembly according to claim 13, wherein the second angle is at least 10°.
 16. The valve assembly according to claim 15, wherein the second angle is at least 20°.
 17. The valve assembly according to claim 16, wherein the second angle is at least 70°.
 18. The valve assembly according to claim 17, wherein the second angle is such that the apertures open at a tangent to an inner surface of the wall of the cage.
 19. The valve assembly according to claim 1, wherein the apertures are quadrilateral in shape, in the shape of a parallelogram or rhomboidal.
 20. The valve assembly according to claim 19, wherein the apertures are in the shape of a parallelogram.
 21. The valve assembly according to claim 20, wherein the apertures are rhomboidal.
 22. The valve assembly according to claim 1, wherein upstream and/or downstream edges of each aperture are curved.
 23. The valve assembly according to claim 1, wherein the cage comprises apertures of a plurality of different sizes.
 24. An apparatus, comprising: a cage assembly for use in a fluid valve assembly, the cage assembly comprising: a cage having apertures therethrough to provide passage for fluid passing from an exterior of the cage to an interior of the cage through a cage wall, the cage having a longitudinal axis, wherein the apertures in the cage wall extend through the cage wall at a first angle to the longitudinal axis of the cage, such that, in use, fluid entering the cage through each aperture is directed into the cage at an angle to the longitudinal axis in an upstream direction; and a plug with a flow guide member, wherein the flow guide member comprises a guide surface extending laterally across an interior of the cage, wherein a radially outer portion of the flow guide member is provided with a first curvilinear circumferential surface portion extending at second angles tangent thereto, wherein the second angles extend in the upstream direction with respect to the longitudinal axis of the cage, a radially inner portion of the flow guide member is provided with a second curvilinear surface portion extending at third angles tangent thereto, wherein the third angles extend in a downstream direction with respect to the longitudinal axis of the cage to redirect the fluid flowing over the first curvilinear surface portion in the downstream direction, wherein the second curvilinear surface portion is a rounded cone.
 25. A valve assembly comprising: a valve housing; an inlet for fluid entering the valve housing; an outlet for fluid leaving the valve housing; a flow control assembly disposed within the valve housing between the inlet and the outlet, whereby fluid entering the valve housing is caused to flow through the flow control assembly, the flow control assembly comprising: a cage having apertures therethrough to provide passage for fluid passing from the inlet to the outlet, the cage having a longitudinal axis and an outlet end, wherein the apertures in the cage extend through the cage at a first angle to the longitudinal axis of the cage, and wherein the first angle is in an upstream direction with respect to the outlet end of the cage; a flow guide member, wherein the flow guide member comprises a guide surface extending laterally across an interior of the cage, wherein a radially outer portion of the flow guide member is provided with a first curvilinear circumferential surface portion extending at second angles tangent thereto, wherein the second angles extend in the upstream direction with respect to the longitudinal axis of the cage, a radially inner portion of the flow guide member is provided with a second curvilinear surface portion extending at third angles tangent thereto, wherein the third angles extend in a downstream direction with respect to the longitudinal axis of the cage, and wherein the second curvilinear surface portion is a rounded cone; and a closure assembly moveable with respect to the cage to open or close each of the apertures through the cage to control the flow of fluid through the cage.
 26. The apparatus of claim 24, wherein the rounded cone defines a first distal end, wherein the distal end is substantially even with a second distal end of the radially outer portion of the flow guide member.
 27. The apparatus of claim 25, wherein the rounded cone defines a first distal end, wherein the distal end is substantially even with a second distal end of the radially outer portion of the flow guide member. 